A scene from Civil War II, a new comic by Marvel. (Courtesy of Marvel)

In recent years, Deadpool, Ant Man and the Guardians of the Galaxy have joined Batman and Superman as household names.

Anyone with a pair of eyes or ears is aware of the crushing avalanche of comic-book movies that seem to perpetually pour into the nation’s theaters. The release schedule for the next several years is fuller than a pastrami sandwich from Katz’s Deli. And they perform with a Michael Phelps-like consistency: “The Avengers” grossed $623 million at the box office, “The Dark Knight” grossed $538 million, and the second “Avengers” movie reached $459 million. That’s just domestically. Worldwide, the numbers jumped to $1.5 billion, $1 billion and $1.4 billion, respectively, according to Box Office Mojo.

Comic books themselves have tread a much more uneven path. According to leading comic-book sales analyst John Jackson Miller, who runs ComiChron, a blog on comic sales, unit sales of the top 300 comics were down for 15 years — some years significantly — after a high in 1997.

Dovetailing unsurprisingly with the rise in movies, though, comic books have seen an increase in sales during each of the past five year. As a fitting cap, recently released sales numbers show that June was the industry’s best-selling month since December 1997.

As explained in Vulture, there are no records of comics bought directly by consumers. Instead, Miller and others track the number of units bought by retailers, in anticipation for demand. Some of those units may never be sold to actual readers.

The system isn’t perfect, but it’s the best we’ve got.

With that in mind, retailers purchased 8.5 million copies of the top 300 comics, the highest number since December 1997, when retailers ordered about 9 million comics, Vulture reported.

That’s a 42 percent increase from five years ago this month, and a 56 percent increase from 15 years ago this month, Miller wrote on his blog.

Much of the increase comes from the releases of the first issues of two major comics — Marvel’s “Civil War II No. 1” and DC’s “Batman No. 1.” Retailers bought 381,737 copies of the former and 280,360 copies of the latter, IGN reported.

These high-profile releases certainly boosted sales numbers, but there are likely many factors in play in the increased popularity in comics.

For one, comic books are more accessible than ever before, partially because of the Internet. Comics, previously purchased at newsstands or in dedicated comic-book stores, can easily be bought and, in some cases, even read digitally — a trend that digital giants have noticed. In 2014, Amazon bought ComiXology, the largest digital comics platform, which sold more than 4 billion pages of comics in 2013, Wired reported. In fact, from 2012 to 2013, digital comic sales rose from $70 million to $90 million, according to the New York Times.

Meanwhile, the number of brick-and-mortar comic-book shops has also risen in recent years, their numbers growing by 4 percent in 2013, according to Publishers Weekly.

Second, the aforementioned hyper-popular films — Marvel’s “Avengers” is the most successful franchise in box-office history — work as a sort of Trojan horse, sneaking comic-book stories into the mainstream. The movies generate interest in their print counterparts, allowing the latter to reach more (and more diverse) readers.

Milton Griepp, chief executive of the pop culture blog ICv2, told Business Insider in 2014, “The movies have helped expand the audience beyond the core young adult male demographic to include females of similar ages, as well as older and younger readers.”

Augie De Blieck Jr., a columnist at Comic Book Resources, agreed that comics have a more diverse readership, though he still thinks that readership is not being catered to enough.

“With the boom in movie and television superheroes, there’s an audience out there that craves this superhero material now,” Blieck told CNBC. “Those people aren’t always being marketed to, like children, women and ‘insert your favorite ethnic minority in the United States here.'”

Finally, the genre is attracting outside talent to write its comic books.

Atlantic magazine writer and social critic Ta-Nehisi Coates followed up his National Book Award-winning “Between the World and Me” not with another biting, controversial tome but with a comic book. Coates, a longtime comic fan, wrote an 11-issue run of “Black Panther.” The Black Panther character, which debuted in 1966, was the first mainstream black comic-book superhero.

“I loved Marvel all my life. As a young person, it was basically one of the first places I really learned to think about writing,” Coates said in an interview with the Atlantic. “So any opportunity to think about writing for Marvel, I just couldn’t turn it down.”

He continued, saying that part of the appeal of comics for him were the escapism they provided.

“I think if you’re like a young man in West Baltimore, and all around you is a considerable amount of powerlessness, you probably have an attraction to people with power,” Coates said. “I could lose myself for long periods of time with comic books.”

So far, his run has certainly elevated the character, and the attention it has garnered arguably raised the profile of comics in general. “Black Panther No. 1,” the first issue in his series, had sold 253,000 copies in April, making it the best-selling comic of the year at the time.

“There have been many Black Panther series over the years from Marvel, but the title has never been one to appear near the top of the sales charts,” Miller wrote.

The record-setting sales in June might not be sustainable. As Vulture noted, first issues tend to sell far more than its sequels (as witnessed by the drop-off in sales for “Black Panther”).

Still, comic-book fans can breathe a bit more easily knowing the trend of rising sales from the past five years appears to be continuing.

Sign up for email updates from the "Confronting the Caliphate" series.